即时通信系统Openfire分析之六:路由表 RoutingTable

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  还是从会话管理说起

  上一章,Session经过预创建、认证之后,才正常可用。认证时,最重要的操作,就是将Session加入到路由表,使之拥用了通信功能。

  添加到至路由表的操作,是在SessionManager中操作的,如下:

  SessionManager.addSession(LocalClientSession session):

public void addSession(LocalClientSession session) {
    // Add session to the routing table (routing table will know session is not available yet)
    routingTable.addClientRoute(session.getAddress(), session);
    // Remove the pre-Authenticated session but remember to use the temporary ID as the key
    localSessionManager.getPreAuthenticatedSessions().remove(session.getStreamID().toString());
    SessionEventDispatcher.EventType event = session.getAuthToken().isAnonymous() ?
            SessionEventDispatcher.EventType.anonymous_session_created :
            SessionEventDispatcher.EventType.session_created;
    // Fire session created event.
    SessionEventDispatcher.dispatchEvent(session, event);
    if (ClusterManager.isClusteringStarted()) {
        // Track information about the session and share it with other cluster nodes
        sessionInfoCache.put(session.getAddress().toString(), new ClientSessionInfo(session));
    }
}

  进入路由表模块, RoutingTableImpl.addClientRoute(session.getAddress(), session)方法:

public boolean addClientRoute(JID route, LocalClientSession destination) {
    boolean added;
    boolean available = destination.getPresence().isAvailable();
    localRoutingTable.addRoute(route.toString(), destination);
    ......
    return added;
}

  从这里可以看出,路由表的底层,是借助LocalRoutingTable类来实现。

  路由表的底层数据结构

  LocalRoutingTable类的成员构成,非常的简单:

Map<String, RoutableChannelHandler> routes = new ConcurrentHashMap<>();

  也就是说,路由表的实质,就是一个Map的数据结构,其Key为JID地址,Velue为RoutableChannelHandler类型报文处理器。

  查看路由表RoutingTableImpl模块中的路由添加方法,可以看到表中存储的是以RoutableChannelHandler衍生出来的几个Session类型,总共提供了三种:

  LocalOutgoingServerSession(用于存储连接本机的远程服务端)、LocalClientSession(用于存储连接到本机的客户端)、RoutableChannelHandler(用于存储组件),类结构如下:

|-- RoutableChannelHandler
    |-- Session
        |-- LocalSession
            |-- LocalClientSession
            |-- LocalServerSession
                |-- LocalOutgoingServerSession

  而LocalRoutingTable内的所有方法,就是一系列对这个Map结构的操作函数,核心的如下几个:

  添加路由:

boolean addRoute(String address, RoutableChannelHandler route) {
    return routes.put(address, route) != route;
}

  获取路由:

RoutableChannelHandler getRoute(String address) {
    return routes.get(address);
}

  获取客户端的Session列表:

Collection<LocalClientSession> getClientRoutes() {
    List<LocalClientSession> sessions = new ArrayList<>();
    for (RoutableChannelHandler route : routes.values()) {
        if (route instanceof LocalClientSession) {
            sessions.add((LocalClientSession) route);
        }
    }
    return sessions;
}

  移除路由

void removeRoute(String address) {
    routes.remove(address);
}

  还有一个每3分钟一次的定时任务,查询并关闭被闲置了的远程服务器Session,在路由表中启动该任务

public void start() {
    int period = 3 * 60 * 1000;
    TaskEngine.getInstance().scheduleAtFixedRate(new ServerCleanupTask(), period, period);
}

  路由表模块 RoutingTable

  路由表是Openfire的核心module之一,RoutingTable接口定义了一系列操作标准,主要围绕路由表进行,提供添加,删除,查询,消息路由等操作,而RoutingTableImpl负责具体实现。

  先来看看RoutingTableImpl的成员列表

/**
 * 缓存外部远程服务器session
 * Key: server domain, Value: nodeID
 */
private Cache<String, byte[]> serversCache;
/**
 * 缓存服务器的组件
 * Key: component domain, Value: list of nodeIDs hosting the component
 */
private Cache<String, Set<NodeID>> componentsCache;
/**
 * 缓存已认证的客户端session
 * Key: full JID, Value: {nodeID, available/unavailable}
 */
private Cache<String, ClientRoute> usersCache;
/**
 * 缓存已认证匿名的客户端session
 * Key: full JID, Value: {nodeID, available/unavailable}
 */
private Cache<String, ClientRoute> anonymousUsersCache;
/**
 * 缓存已认证(包括匿名)的客户端Resource,一个用户,在每一端登录,都会有一个resource
 * Key: bare JID, Value: list of full JIDs of the user
 */
private Cache<String, Collection<String>> usersSessions;

private String serverName;                              // 服务器的域名
private XMPPServer server;                              // XMPP服务
private LocalRoutingTable localRoutingTable;            // 路由表底层
private RemotePacketRouter remotePacketRouter;          // 远程包路由器
private IQRouter iqRouter;                              // IQ包路由器
private MessageRouter messageRouter;                    // Message包路由器
private PresenceRouter presenceRouter;                  // Presence包路由器
private PresenceUpdateHandler presenceUpdateHandler;    // 在线状态更新处理器

  成员列表中,除了LocalRoutingTable之外,还定义了一堆的缓存。这些缓存干嘛用?

  Openfire支持集群机制,即在多台服务器上分别运行一个Openfire实例,并使各个实例的数据同步。算法一致,数据一致,用户不管连接到任意一台服务器,效果就都一样。

  集群中的数据同步,除了数据库之外,其他的都是用通过缓存来处理,而上面的这些缓存正是集群同步的一部分,用于同步用户路由信息,每个服务器都会有缓存的副本。

  总的来说,LocalRoutingTable用于存储本机的路由数据,而Cache中是存储了整个集群的路由数据。

  但是,需要注意的一点,LocalRoutingTable与Cache,这两者的数据结构并不相同:

  (1)LocalRoutingTable中记录了本机中所有的Session实例,可以用来通信

  (2)Cache中只存储了用户路由节点信息,需要通过集群管理组件来获取Session实例

  路由表的操作

  路由表的操作,实际上就是在会话管理中,对会话实例的操作。为免与上面混淆,这一节的功能说明,以会话代称。

  添加路由(会话)

  代码如下:

@Override
public boolean addClientRoute(JID route, LocalClientSession destination) {
    boolean added;
    boolean available = destination.getPresence().isAvailable();
    
    // 加入到路由表
    localRoutingTable.addRoute(route.toString(), destination);
    
    // 若为匿名客户端,添加到anonymousUsersCache、usersSessions缓存队列中
    if (destination.getAuthToken().isAnonymous()) {
        Lock lockAn = CacheFactory.getLock(route.toString(), anonymousUsersCache);
        try {
            lockAn.lock();
            added = anonymousUsersCache.put(route.toString(), new ClientRoute(server.getNodeID(), available)) ==
                    null;
        }
        finally {
            lockAn.unlock();
        }
        // Add the session to the list of user sessions
        if (route.getResource() != null && (!available || added)) {
            Lock lock = CacheFactory.getLock(route.toBareJID(), usersSessions);
            try {
                lock.lock();
                usersSessions.put(route.toBareJID(), Arrays.asList(route.toString()));
            }
            finally {
                lock.unlock();
            }
        }
    }
    
    // 非匿名客户端,添加到usersCache、usersSessions缓存队列中
    else {
        Lock lockU = CacheFactory.getLock(route.toString(), usersCache);
        try {
            lockU.lock();
            added = usersCache.put(route.toString(), new ClientRoute(server.getNodeID(), available)) == null;
        }
        finally {
            lockU.unlock();
        }
        // Add the session to the list of user sessions
        if (route.getResource() != null && (!available || added)) {
            Lock lock = CacheFactory.getLock(route.toBareJID(), usersSessions);
            try {
                lock.lock();
                Collection<String> jids = usersSessions.get(route.toBareJID());
                if (jids == null) {
                    // Optimization - use different class depending on current setup
                    if (ClusterManager.isClusteringStarted()) {
                        jids = new HashSet<>();
                    }
                    else {
                        jids = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
                    }
                }
                jids.add(route.toString());
                usersSessions.put(route.toBareJID(), jids);
            }
            finally {
                lock.unlock();
            }
        }
    }
    return added;
}

  主要两步:

  (1)添加到路由表
  (2)添加到对应的缓存中

  移除路由(会话)

  代码如下:

@Override
public boolean removeClientRoute(JID route) {
    boolean anonymous = false;
    String address = route.toString();
    ClientRoute clientRoute = null;
    
    // 从缓存中移除客户端的Session信息
    Lock lockU = CacheFactory.getLock(address, usersCache);
    try {
        lockU.lock();
        clientRoute = usersCache.remove(address);
    }
    finally {
        lockU.unlock();
    }
    if (clientRoute == null) {
        Lock lockA = CacheFactory.getLock(address, anonymousUsersCache);
        try {
            lockA.lock();
            clientRoute = anonymousUsersCache.remove(address);
            anonymous = true;
        }
        finally {
            lockA.unlock();
        }
    }
    if (clientRoute != null && route.getResource() != null) {
        Lock lock = CacheFactory.getLock(route.toBareJID(), usersSessions);
        try {
            lock.lock();
            if (anonymous) {
                usersSessions.remove(route.toBareJID());
            }
            else {
                Collection<String> jids = usersSessions.get(route.toBareJID());
                if (jids != null) {
                    jids.remove(route.toString());
                    if (!jids.isEmpty()) {
                        usersSessions.put(route.toBareJID(), jids);
                    }
                    else {
                        usersSessions.remove(route.toBareJID());
                    }
                }
            }
        }
        finally {
            lock.unlock();
        }
    }
    
    // 将对应客户端的Session信息,移出路由表
    localRoutingTable.removeRoute(address);
    return clientRoute != null;
}

  操作与添加类似:
  (1)移除缓存里的路由信息
  (2)移除路由表中的信息

  获取路由(会话)

@Override
public ClientSession getClientRoute(JID jid) {
    // Check if this session is hosted by this cluster node
    ClientSession session = (ClientSession) localRoutingTable.getRoute(jid.toString());
    if (session == null) {
        // The session is not in this JVM so assume remote
        RemoteSessionLocator locator = server.getRemoteSessionLocator();
        if (locator != null) {
            // Check if the session is hosted by other cluster node
            ClientRoute route = usersCache.get(jid.toString());
            if (route == null) {
                route = anonymousUsersCache.get(jid.toString());
            }
            if (route != null) {
                session = locator.getClientSession(route.getNodeID().toByteArray(), jid);
            }
        }
    }
    return session;
}

  从上面的方法代码中可以看到,获取路由的方法是:先查找本地路由表,若获取不到对应Session时,则通过集群获取。RemoteSessionLocator是用于适配不同的集群组件所抽象的接口,为不同集群组件提供了透明处理。

  至于如何从集群中获取Session,主要就在于sersCache和anonymousUsersCache这两个cache,它们记录了每个客户端的路由节点信息,通过它可以取得对应的Session实例。

  消息路由

  根据发送的形式,分为两种:一是广播、二是单点路由

  1、以广播的形式,向所有在线的客户端发送消息

@Override
public void broadcastPacket(Message packet, boolean onlyLocal) {
    // Send the message to client sessions connected to this JVM
    for(ClientSession session : localRoutingTable.getClientRoutes()) {
        session.process(packet);
    }

    // Check if we need to broadcast the message to client sessions connected to remote cluter nodes
    if (!onlyLocal && remotePacketRouter != null) {
        remotePacketRouter.broadcastPacket(packet);
    }
}

  2、单点发送的形式,向某个指定的客户端发送消息

@Override
public void routePacket(JID jid, Packet packet, boolean fromServer) throws PacketException {
    
    boolean routed = false;
    try {
        if (serverName.equals(jid.getDomain())) {
            // Packet sent to our domain.
            routed = routeToLocalDomain(jid, packet, fromServer);
            Log.info("routeToLocalDomain");
        }
        else if (jid.getDomain().endsWith(serverName) && hasComponentRoute(jid)) {
            // Packet sent to component hosted in this server
            routed = routeToComponent(jid, packet, routed);
            Log.info("routeToComponent");
        }
        else {
            // Packet sent to remote server
            routed = routeToRemoteDomain(jid, packet, routed);
            Log.info("routeToRemoteDomain");
        }
    } catch (Exception ex) {
        // Catch here to ensure that all packets get handled, despite various processing
        // exceptions, rather than letting any fall through the cracks. For example,
        // an IAE could be thrown when running in a cluster if a remote member becomes 
        // unavailable before the routing caches are updated to remove the defunct node.
        // We have also occasionally seen various flavors of NPE and other oddities, 
        // typically due to unexpected environment or logic breakdowns. 
        Log.error("Primary packet routing failed", ex); 
    }

    if (!routed) {
        if (Log.isDebugEnabled()) {
            Log.debug("Failed to route packet to JID: {} packet: {}", jid, packet.toXML());
        }
        if (packet instanceof IQ) {
            iqRouter.routingFailed(jid, packet);
        }
        else if (packet instanceof Message) {
            messageRouter.routingFailed(jid, packet);
        }
        else if (packet instanceof Presence) {
            presenceRouter.routingFailed(jid, packet);
        }
    }
}

  路由表中的功能,最后由SessionManager集中处理,详见上一章的分析,这里不再赘述。

  特点提一点,比较有用:路由表做为一个module已经在Openfire主服务启动时完成实例化,所以,在自定义的插件、或者其他任何需要发送消息的地方,只需选择调用如下两个方法中之一,即可完成消息发送:

XMPPServer.getInstance().getRoutingTable().routePacket(jid, packet, fromServer);

XMPPServer.getInstance().getRoutingTable().broadcastPacket(packet, onlyLocal);

  而消息发送中,最后消息如何送到网卡实现发送,在第三章《消息路由》中已经详细分析,同样不再赘述。


 

  本章就到此结束,OVER!

 

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